Such audio systems are for instance used in mobile applications like mobile phones or cars. Document EP 0 471 990 B1 discloses such an audio system that comprises an electro-acoustic transducer or speaker with a banked winding consisting of a first coil and a second coil. A first driver circuit is connected to the first coil and a second driver circuit is connected to the second coil to independently feed audio signals to the first and the second coil. In one embodiment disclosed in the document, a stereo audio signal is fed to the speaker, wherein the left audio signal is fed by the first driver circuit to the first coil and the right audio signal is fed by the second driver circuit to the second coil of the speaker. In another embodiment disclosed in the document, the speaker is used in a car, wherein the audio signal from the radio is fed to the first coil and the audio signal from the telephone is fed to the second coil. In both of these disclosed embodiments, audio signals are fed independently to the first and the second coil to achieve an overlaid acoustic signal.
Electro-acoustic transducers are in general hampered by mechanical and electrical nonlinearities that lead to all kind of different acoustic distortions. There are prior art speakers that use the coil of the speaker in a sensor operating mode to sense an electrical signal induced and to process the sensor signal based on a mathematical model of the speaker. A drawback for these solutions is the need for correct static loudspeaker parameters and the restriction of velocity measurement of the system.